Microbial growth inhibiting material and method of forming

ABSTRACT

The invention includes methods of inhibiting microbial growth in a well. A packing material containing a mixture of a first material and an antimicrobial agent is provided to at least partially fill a well bore. One or more access tubes are provided in an annular space around a casing within the well bore. The access tubes have a first terminal opening located at or above a ground surface and have a length that extends from the first terminal opening at least part of the depth of the well bore. The access tubes have a second terminal opening located within the well bore. An antimicrobial material is supplied into the well bore through the first terminal opening of the access tubes. The invention also includes well constructs.

RELATED APPLICATIONS

This application is a divisional of pending U.S. patent application Ser.No. 09/991,331, filed on Nov. 14, 2001.

CONTRACTUAL ORIGIN OF THE INVENTION

This invention was made with United States Government support underContract No. DE-AC07-99ID13727 awarded by the United States Departmentof Energy. The United States Government has certain rights in theinvention.

TECHNICAL FIELD

The present invention pertains to well constructions and methods ofinhibiting microbial growth in wells.

BACKGROUND OF THE INVENTION

The presence of microbial growth can cause bio-fouling and plugging ofwells. Such plugging can occur both in vadose-zone wells and insaturated-zone wells. Vadose-zone wells are wells having a well borethat does not extend into the water table, and include, for example,vadose-zone monitoring wells, vapor extraction wells and injectionwells. Saturated-zone wells have a well bore that extends into the watertable such as, for example, ground water monitoring wells, productionwells and irrigation wells. Plugging of a well may occur by plugging ofstructures within the well such as the filter pack, screening, piping,or pumps. Plugging may also occur by the plugging of the surroundinggeological media. Such plugging is caused by an accumulation ofmicrobial growth, by an accumulation of microbial extracellularmaterial, or both.

Once a well has become bio-fouled or plugged, treatment of the well toeliminate microbial growth and remove plugging is often difficult andineffective. Remedial chemical treatments, such as an introduction of ahighly concentrated chlorine solution into the well, often fail due tothe difficulty in forcing the solution through an already plugged well.Once bio-fouling has occurred, replacement of the effected structure isoften required. Severe bio-fouling and plugging may require replacementof the entire well at great expense.

Accordingly, it is desirable to provide well constructions andpreventative treatment methods designed to minimize unwanted microbialgrowth in wells.

SUMMARY OF THE INVENTION

In one aspect, the invention encompasses a method of inhibitingmicrobial growth in a well. A well bore is provided. A first material ismixed with an antimicrobial agent to form a packing material. Thepacking material is used to fill at least a portion of the well bore.

In another aspect, the invention encompasses a material for packingwithin a well. The material for packing the well includes either sand orgravel, or both. The material for packing the well also includes anantimicrobial agent. The antimicrobial agent can be in powdered form, ingranular form, in pellet form, in tablet form, in precipitate form, orcan be a mixture of two or more of these forms.

In another aspect, the invention encompasses an additional method ofinhibiting microbial growth in a well. A well bore is provided that hasa depth extending from a ground surface. A casing is provided within thewell bore and is at least partially surrounded by an annular space. Oneor more access tubes are provided within the annular space of the wellbore, outside the casing. The access tubes have a first terminal openinglocated at or above the ground surface and have a length that extendsfrom the first terminal opening at least part of the depth of the wellbore. The access tubes have a second terminal opening located within thewell bore. An antimicrobial material is supplied into the well borethrough the first terminal opening of the access tubes.

In still another aspect, the invention encompasses a well constructionhaving inhibited microbial growth. The well construction includes a wellbore and a well casing within the well bore. The casing has a terminalend within the well bore and has a screened portion that extends fromthe terminal end to a first elevation within the well bore. Multipleaccess tubes encircle the casing within the well bore. The access tubeshave a terminal end within the bore and have a perforated segmentextending from the terminal end to a second elevation within the wellbore. The well bore contains a layer of packing material comprising afirst antimicrobial agent mixed with either sand or gravel, or mixedwith both sand and gravel. The layer of packing material fills the wellbore to a third elevation. The well construction includes a secondantimicrobial agent which, when provided through an access tube, is ableto pass from within an access tube into the packing material through theperforated segment of the access tube.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 shows a diagram of a well construction formed in accordance withthe methodology of the present invention.

FIG. 2 is an enlarged view of the encircled region in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

The present invention is described with reference to a well construction10 in FIGS. 1 and 2. Referring to FIG. 1, well construction 10 comprisesa well bore 12. A packing material 16 at least partially fills well bore12. Packing material 16 comprises a first material 14 and anantimicrobial agent 15, as shown in FIG. 2. Prior to use in the wellbore, packing material 16 can be formed by mixing first material 14 withantimicrobial agent 15.

A variety of materials are available for use as first material 14 forpurposes of the present invention. Exemplary materials include sand,gravel, or a mixture thereof.

Antimicrobial agent 15 can comprise a solid and can be mixed with firstmaterial 14 such that packing material 16 contains antimicrobial agent15 from about 0.5% to about 30% (by volume). Exemplary solid forms forantimicrobial agent 15 for purposes of the present invention includeprecipitate form, powder form, tablet form, granular form or pelletform.

Mixing of antimicrobial agent 15 with first material 14 can comprisecoating the first material with the antimicrobial agent. Coating offirst material 14 can be performed by mixing a powdered antimicrobialagent with the first material. Coating can also be performed bydissolving any of the solid forms of antimicrobial agent, mixing thedissolved antimicrobial agent with the first material, andre-precipitating the antimicrobial agent. The solid antimicrobial agentscan be dissolved in an organic or an inorganic solvent based upon thesolubility properties of the specific agent. The resulting precipitatecan form a coating on first material 14. Alternatively, the mixing cancomprise forming a composite mixture of the first material and one ormore of, for example, antimicrobial powder, antimicrobial tablets,antimicrobial granules, and antimicrobial pellets.

At least some of the antimicrobial agent 15 utilized for purposes of thepresent invention can be delayed release. A delayed releaseantimicrobial agent can include, for instance, solid forms of anantimicrobial agent that dissolve slowly in water. For example, a tabletform, a granular form or a pellet form of antimicrobial compound candissolve more slowly than the powder form of the same antimicrobialcompound. In addition, encapsulation or coating of any of the solidforms listed can further decrease the rate of dissolving in water.Numerous encapsulating or coating material is available for utilizationin the present invention, including coating material comprising, forinstance; proteins, polysaccharide, starches, waxes, fats, natural andsynthetic polymers, and resins.

Numerous compounds from a variety of classes of antimicrobial compoundsof can be utilized for purposes of the present invention. Exemplaryclasses of such antimicrobial compounds include chlorine release typecompounds, antimicrobial amines, and antimicrobial metals. Chlorinerelease type compounds include, for instance, compounds that can releasechlorine when the compound reacts with water. Specific chlorine releasecompounds include, for example, calcium hypochlorites,trichloroisocyanurate, dichloroisocyanurate.

Specific types of compounds within the class of antimicrobial amines forpurposes of the present invention include, quaternary ammonia compoundsand N-halamines such as;poly-acrylonitrile-co-4(acryloxymethyl)-4-ethyl-2-oxazolidinone latex,poly-vinyl chloride-co-4-(acryloxymethyl)-4-ethyl-2-oxazolidinone latex,poly-styrene-co-4-(acryloxymethyl)-4-ethyl-2-oxazolidinone latex,poly-vinyl acetate-co-4-(acryloxymethyl)-4-ethyl-2-oxazolidinone latex,poly-acrylonitrile-g-4-(acryloxymethyl)-4-ethyl-2-oxazolidinone latex,poly-vinyl chloride-g-4-(acryloxymethyl)-4-ethyl-2-oxazolidinone latex,poly-styrene-g-4-(acryloxymethyl)-4-ethyl-2-oxazolidinone latex,poly-vinyl acetate-g-4-(acryloxymethyl)-4-ethyl-2-oxazolidinone latex,poly-vinyl alcohol-g-4-(acryloxymethyl)-4-ethyl-2-oxazolidinone latexandpoly(1,3,5-trichloro-6-methyl-6-(4′-vinylphenyl)-1,3,5-triazine-2,4-dione.

Specific examples of agents within the class of antimicrobial metalswhich can be utilized for purposes of the present invention include, butare not limited to, silver, zinc and copper.

The present invention encompasses embodiments of packing material 16wherein the packing material comprises a single solid form ofantimicrobial agent and embodiments wherein packing material 16comprises multiple solid forms of an antimicrobial agent. In addition,packing material 16 can comprise a single antimicrobial compound or cancomprise multiple antimicrobial compounds from one or more of theclasses of compounds listed. It can be beneficial to have multiple formsof solid antimicrobial present in packing material 16 to provide bothshort term and long term microbial growth inhibition. For example, ifantimicrobial agent 15 comprises both a powder form and a tablet form,the powder form can dissolve quickly, thereby providing an immediatemicrobial growth inhibiting effect, while the tablet form can dissolvemore slowly, providing a delayed or long term effect relative to thepowder form. For similar reasons, it can be beneficial for antimicrobialagent 15 to comprise multiple compounds or classes of compounds whichdissolve at different rates or vary in duration of microbial inhibitingeffects.

The well construction 10 of the present invention can comprise avadose-zone well or a saturated-zone well. Well bore 12 can, therefore,comprise a depth that extends from a ground surface 30 into thevadose-zone 28 (not shown), or, as shown in FIG. 1., from ground surface30 into the saturated-zone 26. Where the well is a vadose-zone well,because the bore does not extend into the water table, water forreacting with or dissolving an antimicrobial agent is provided by forexample, condensation, infiltration, or unsaturated flow. The rate ofdissolving of any given form of an antimicrobial agent, therefore, willbe less than the corresponding rate in a saturated-zone well. The formof solid to be utilized in a specific well construction can bedetermined accordingly.

In the shown embodiment, well construction 10 comprises a casing 18within well bore 12. It is to be understood that the present inventionencompasses an open-bore well construction that lacks casing 18 (notshown). Casing 18 can be at least partially surrounded by an annularspace 20 and can comprise a screened portion 22 that extends from aterminal end 48, located within well bore 12, to a first elevationwithin the well bore. Packing material 16 can fill at least part ofannular space 20 around well casing 18 to a second elevation within thewell bore. The second elevation can be greater than the first elevationsuch that packing material 16 at least covers screened portion 22 ofcasing 18.

Additionally, well construction 10 can comprise a seal layer 23 whichcan seal packing material 16. Seal layer 23 can comprise, for example,bentonite, concrete, neat cement, or a mixture thereof. Whether or notwell construction 10 comprises seal layer 23, well construction 10 cancomprise a fill material 24 such as, for instance, concrete, bentonite(in dry form or comprised in a slurry), neat cement, or a mixture ofcement and bentonite. Fill material 24 can at least partially fill anyannular space 20 remaining in the well bore beyond the portion filledwith packing material 16.

In addition to the features described above, the invention encompasses awell construction 10 comprising at least one access tube 32 within wellbore 12. In embodiments comprising well casing 18, the at least oneaccess tube can be positioned outside casing 18 within annular space 20.Access tubes 32 have a first terminal opening 34 that is preferablylocated above ground surface 30. Access tubes 32 extend at least part ofthe depth of well bore 12, from first terminal opening 34, to a secondterminal opening 36 within the well bore. Well construction 10 cancomprise an antimicrobial agent 39 that is distinct from theantimicrobial agent 15 in packing material 16, at least initially.

Access tubes 32 are not limited to a specific number of tubes, nor isplacement of such tubes limited to a specific distribution within wellbore 12. The number of tubes can be, for instance, from about 2 to about10 access tubes. Access tubes 32 can have a diameter from about 0.25inches to about 1.5 inches. The access tubes can be distributed, forexample, around the circumference of casing 18 and can be equally spacedaround the circumference with respect to each other.

In addition to the above features, access tubes 32 of well construction10 can comprise a perforated segment 40 extending from second terminalopening 36 to a third elevation within well bore 12. The third elevationcan be less than the second such that perforated segment 40 is entirelycovered by packing material 16. Access tubes 32 can comprise a cap 42 toclose second terminal opening 36, and a removable cap 44 that coversfirst terminal opening 34.

Antimicrobial material 39 can be supplied into well 10 through the firstterminal opening 34 of access tubes 32. Once antimicrobial agent 39 isadded through terminal opening 34, antimicrobial agent 39 can be able topass from within access tube 32 into packing material 16 throughperforated segment 40 of access tube 32.

Antimicrobial material 39 can be supplied at time intervals. Exemplarytime intervals for purposes of the present invention can be from betweenabout 2 months and about 12 months. During the time interval betweensupplying antimicrobial agent 39, the first terminal opening 34 ofaccess tubes 32 can be reversibly capped 44.

Antimicrobial agent 39 is not limited to any specific material or form.Antimicrobial agent 39 can comprise, for example, one or more of thesolid forms discussed above with respect to antimicrobial agent 15.Antimicrobial agent 39 can also comprise one or both of a gasantimicrobial agent and a liquid antimicrobial agent, or can comprise acombination of one or more of a gas antimicrobial agent, a liquidantimicrobial agent and a solid antimicrobial agent. Exemplary gasantimicrobial agents for purposes of the present invention includechlorine and ozone. Exemplary liquid antimicrobial agents, for purposesof the present invention include one or more of iodine, bromine or adissolved form of any of the chlorine release type compound discussedabove.

Where antimicrobial agent 39 comprises a gas or a liquid, supplying ofantimicrobial agent 39 through first terminal opening 34 can comprisepressure pumping the gas or liquid through first terminal opening 34.Alternatively, the gas or liquid may be pushed through the access tubeby utilizing a pressurized air stream that can be flowed through firstterminal opening 34 of access tubes 32, or by inserting a slotted tubethrough the first terminal opening to sift the antimicrobial agentthrough perforated segment 40 of the access tubes.

As shown in FIG. 1, well constructions 10 encompassed by the presentinvention include constructions comprising the described well packingmaterial 16 containing antimicrobial agent 15, and simultaneouslycomprising access tubes 32 and the described antimicrobial agent 39, ina single well. Where a single well comprises both antimicrobial agent 15and antimicrobial agent 39, the two antimicrobial agents can be the sameor can differ. As discussed above, it can be beneficial to provide amultiple forms of antimicrobial compounds and/or multiple compoundswithin a single well.

Well constructions encompassed by the present invention also includeconstructions comprising access tubes 32 and antimicrobial agent 39 inthe absence of packing material 16 and antimicrobial 15 (not shown). Theinvention also contemplates well constructions comprising packingmaterial 16 containing antimicrobial agent 15, and comprising an absenceof antimicrobial agent 39, and well constructions comprising packingmaterial 16 and an absence of access tubes 32. The use of packingmaterial 16 of the present invention is not intended to be limited touse within a well.

It is to be understood that the present invention contemplatesadaptation of the above described methods and well constructs forbio-remedial and bio-venting wells. Bio-venting and bio-remedial wellsutilize bacteria to perform functions in furtherance of the purposes ofthe well. However, growth of these microbes is preferentiallyconstrained to the surrounding geological structures rather than withinthe well bore. Accumulation of such microbes or extracellular materialwithin the well bore can detrimentally effect the functioning of thewell, and lead to plugging.

The above described methods can be used to inhibit microbial growthwithin the well bore of a bio-venting or bio-remedial with limitedadverse effects on the microbial population in the surroundinggeological structures. For example, an antimicrobial with limiteddiffusion properties due to a low solubility, such as for instance apolymeric amine, can be utilized within the well bore to minimizediffusion into the surrounding geological structures. The antimicrobialeffects can thereby be limited to, or localized within, the well bore.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A method of forming a well packing material comprising: mixing anantimicrobial agent with one or both of sand and gravel, wherein theantimicrobial agent comprises one or more of a dissolved form, apowdered form, a granular form, a pellet form, and a tablet form; andwherein the antimicrobial agent content in the packing material is fromabout 0.5% to about 30%, by volume.
 2. The method of claim 1 wherein atleast some of the antimicrobial agent is encapsulated.
 3. The method ofclaim 1 wherein the antimicrobial agent comprises one or more of achlorine release compound, an antimicrobial amine, and a metalinhibitor.
 4. The method of claim 1 wherein the antimicrobial agentcomprises a powdered form and wherein the mixing comprises coating theone or more of sand and gravel with the powdered form.
 5. The method ofclaim 1 wherein the antimicrobial agent comprises a dissolved form, themethod further comprising; adding a solution comprising the dissolvedform of antimicrobial agent to the one or both of sand and gravel,wherein the mixing comprises mixing the one or more of sand or gravelwith the solution; and forming a precipitate from the dissolved form ofantimicrobial agent, wherein the precipitate forms a coating on the oneor more of sand and gravel.
 6. A microbial growth inhibiting materialcomprising: at least one of sand or gravel; and an antimicrobial agent,wherein the antimicrobial agent comprises one or more of a precipitateform, a powder form, a tablet form, a granular form, and a pellet form,and comprises one or more of a chlorine releasing compound, anantimicrobial metal, and an antimicrobial amine.
 7. The material ofclaim 6 wherein the antimicrobial agent comprises one or more of aprecipitate form and a powder form, and wherein the at least one of sandor gravel is coated with one or both of the precipitate and the powder.8. The material of claim 6 wherein at least some of the antimicrobialagent is delayed release.
 9. The material of claim 6 wherein theantimicrobial agent comprises a chlorine releasing compound selectedfrom the group consisting of calcium hypochlorites,trichloroisocyanurate, dichloroisocyanurate.
 10. The material of claim 6wherein the antimicrobial agent comprises an antimicrobial metalselected from the group consisting of silver, copper and zinc
 11. Thematerial of claim 10 wherein the antimicrobial agent comprises anantimicrobial amine, wherein the antimicrobial amine is selected fromthe group consisting of quaternary ammonia compounds and N-halamines.12. The material of claim 1 wherein the at least some of theantimicrobial agent is encapsulated.